The present invention relates generally to an occupant restraint system for motor vehicles. More particularly, the present invention is directed to a safety belt retractor having a timing clutch mechanism capable of resetting the timing of an automatic locking mechanism after controlled yielding of an energy management mechanism.
As part of the occupant restraint system currently used in motor vehicles, several different types of safety belt retractors are available which provide enhanced occupant comfort and/or different functional modes. For example, one type of safety belt retractor, often referred to as an emergency locking retractor (ELR), includes a latch mechanism which is automatically actuated in response to certain high acceleration conditions to prevent payout of the safety belt. In some emergency locking retractors, the latch mechanism is actuated by an inertia-sensitive actuator when the vehicle is subjected to a certain deceleration level. In other emergency locking retractors, the latch mechanism is actuated by a web-sensitive actuator when the belt is withdrawn from the spool at a rate exceeding a designated level.
Another type of safety belt retractor, commonly referred to as an automatic locking retractor (ALR), is used for securely tethering a portable child seat to the vehicle seat. Many automatic locking retractors include a holdout mechanism which is selectively activated by withdrawing a predetermined length of the safety belt. Once the predetermined length of the safety belt has been withdrawn, the holdout mechanism engages a latch mechanism to prevent subsequent payout of the safety belt. Thereafter, this locking function is cancelled by disengaging the latch mechanism in response to retraction of the safety belt to its stowed position. Typically, the holdout mechanism includes a timing device for measuring the length of safety belt withdrawn and retracted and controlling actuation and subsequent cancellation of the locking function. In some vehicular seat applications, a dual-mode safety belt retractor is used which normally operates as an ELR retractor until the holdout mechanism is actuated for switching to operation as an ALR retractor.
Safety belt retractors may also include an energy management mechanism which functions to absorb a portion of the energy (i.e. impact loads) transferred from the safety belt to the seat occupant during a collision. For example, some energy management retractors include a torsion bar having a first end fixed to the spool. During a collision, the latch mechanism engages the second end of the torsion bar. As such, the loading force applied by the seat occupant to the safety belt is transferred to the spool and causes the first end of the torsion bar to yield (i.e. twist) relative to the latched second end. Such torsional yielding of the torsion bar results in a limited amount of additional rotation of the spool which, in turn, permits a corresponding additional length of the safety belt to be withdrawn from the retractor. The controlled payout of additional belt in response to loading on the safety belt effectively dampens the amount of impact energy transferred to the seat occupant. However, this additional length of belt may affect subsequent operation of the timing device associated with the holdout mechanism by requiring an additional amount of the safety belt to be withdrawn and retracted to respectively actuate and cancel the locking function.
In view of the above, it is an object of the present invention to provide a safety belt retractor equipped with an energy management mechanism capable of yielding to absorb a portion of the impact energy generated during a collision, and a timing clutch mechanism capable of resetting the timing assembly of a holdout mechanism in response to full retraction of the safety belt after the energy management mechanism has yielded.
Accordingly, the present invention is directed to a safety belt retractor comprised of a spool, a belt wound on the spool, a ratchet wheel, a torsion bar interconnecting the spool to the ratchet wheel and which is capable of yielding in response to loading exerted on the belt when the ratchet wheel is locked against rotation, and an emergency locking mechanism normally operable in a released mode to permit payout of the belt and which is automatically shifted into a locked mode for locking the ratchet wheel against rotation to prevent payout of the belt in response to the occurrence of a high acceleration condition. The safety belt retractor also includes a holdout mechanism which is normally operable in an ELR mode to permit operation of the emergency locking mechanism and which can be selectively shifted into an ALR mode for locking the ratchet wheel against rotation to prevent further payout of the belt after a predetermined length of the belt has been withdrawn from the spool. Subsequent retraction of the predetermined length of the belt shifts the holdout mechanism from its ALR mode into its ELR mode. A timing assembly associated with the holdout mechanism functions to determine when the predetermined length of the belt has been withdrawn or retracted for controlling engagement and disengagement of a latch mechanism. A timing clutch mechanism interconnects the torsion bar to the timing assembly and is normally operable for driving the timing assembly in response to withdrawal and retraction of the belt. The timing clutch mechanism is further operable to permit relative movement between the torsion bar and the timing assembly for resetting the timing assembly to a predefined set position in response to full retraction of the belt after the torsion bar has yielded. As such, the timing clutch mechanism functions to maintain the predetermined length of the belt required for selective actuation of the holdout mechanism in a manner which is independent of yielding of the torsion bar.